off set on a stock 72 dart

Actual data on my 68 cuda, not what-ifs:

The car came with Centerline SBP 15 X 8-1/2" wheels in the rear with 255-60 X 15 BFG radials.
I measured the BS of the wheels at 4-7/8".
Rear was an a-body 8-3/4".
The car came with 5/16" wheel spacers. The holes had been "modified" to fit the 4" bolt pattern.
Trying the wheels and tires w/o the spacers resulted in the side wall of the tires just kissing the springs.
My car needed those spacers with that particular wheel/tire combo.

When I converted the rear to Large Bolt Pattern, the shortened C-body axles added 3/8" to the track on both sides. In other words, the face of the brake drum is now 3/8" further from the springs on both sides. Same housing, just different axles and brake drums. (now 10" x 2-1/2")

Your results may vary depending on production tolerances. If you are going to run your tires with limited clearance, I would recommend poly spring shackle bushing to help eliminate any side ways slop. I got mine from Mancini racing. 7/8" diameter fits the A-body spring eyes.